The venous valves found throughout the venous system assist the flow of blood through the veins and returning to the heart by preventing blood flow reversal. As a majority of venous blood flow is against gravity while a person is standing, incompetent or destroyed venous valves often result in adverse medical conditions, especially in the lower extremities. For example, deep venous hypertension may occur and give rise to clots, lymphedema, skin discoloration, varicose veins and venous ulcers.
The leading cause of venous valve incompetence is venular dilation. When a vein loses elasticity and becomes dilated, the valve cusps become too radially displaced from each other to coapt and prevent backflow. The cusps themselves, however, may not be damaged or stressed, such that restoring elasticity to the vein, or otherwise mechanically restricting the dilation, would allow the cusps to coapt and regain function.
Another type of venous valve incompetence results from damaged cusps. This condition may arise in the presence or absence of dilated veins. Damaged valves must be replaced in order to restore the function of the vein segment.
Reparation of damaged or otherwise incompetent venous valves has been largely limited to autograft procedures. Autograft procedures, though effective, are undesirable as they require the location and excision of healthy, autologous vein segments from other areas of the body. The excised segment must nearly match the size of the segment being replaced, making the location of a replacement vein a sometimes difficult task. An alternative to harvesting healthy vein segments having functional venous valves would be readily advantageous.
Developing a prosthetic or bioprosthetic valve that exhibits, if not improves upon, the functioning characteristics of healthy, natural valves is a task ripe with obstacles. For instance, the venous valves of the lower extremities are very thin. As the veins themselves are narrow, a prosthetic valve would require cusps which are also very thin, to avoid disrupting the blood flow past the valve. The prosthetic cusps, in addition to being thin, must perform to prevent blood flow reversal. Adequate performance necessarily means closing and opening as many as one hundred thousand times a day.
Additionally, the valve must be predictably accepted by the body and remain functional for many years. If the body rejects the valve, or if it malfunctions, many complications could arise, requiring a second surgery to remove the prosthetic valve and repair the vein segment using an alternative method.